[185.15] The Formation of Massive Stars: Accretion Not Mergers?

L. Lanz (U. Maryland), S. E. Strom, S. C. Wolff (NOAO)

Two mechanisms have been proposed to account for the
formation of massive stars: 1) an accretion process similar
to the one that has been shown to apply to low mass stars;
or 2) the merger of already formed protostars. If massive
stars form by mergers, one might expect to find a systematic
difference in the angular momentum of high and low mass
stars; specifically, mergers are likely to lead to high
values of angular momentum.

Spectroscopic observations of massive stars in NGC 6611 have
been used to measure values of vsini. Stellar models have
then been used to calculate the specific angular momentum
(Jsini/M) for each star. When combined with vsini
measurements for lower mass pre-main sequence stars on
convective tracks in Orion, the data show that the upper
limits on Jsini/M plotted as a function of M follow a simple
power law throughout the mass range from 0.1-50 solar
masses. The absence of any discontinuity in specific angular
momentum suggests that there is a single mechanism for star
formation throughout this entire mass range.

This research was supported in part by the NOAO/KPNO
Research Experiences for Undergraduates (REU) Program, which
is funded by the National Science Foundation through
Scientific Program Order No. 3 (AST-0243875) of the
Cooperative Agreement No. AST-0132798 between the
Association of Universities for Research in Astronomy (AURA)
and the NSF.